James readman



(No Model.) I

J. READMAN.

Mariner's and Azimuth Compass.

No. 243,460. Patented une 28, 188].

c #nccccXZ/g/ l INVENTOR:

WITNESSES: J M %.W B g ZS Attorneys,

u. FEIIRS PMo-WWW. Wnlinflul, n a

I v UNITED STATES I PATENT OFFICE.

JAMES READMAN, OF NORTON, COUNTY OF DURHAM,

ENGLAND.

M A RINERS AND AZIMUTH COMPASS.

SPECIFICATION forming part of Letters Patent No. 243,460, dated Application filed March 28, 1881.

December 1, 1880, No. 5,007.

In mariners and azimuth compasses as now made and used the motions of the compasscards produce currents of air within the compass-bowl, so that the compass cannot be relied upon to give a true indication; and this is equally true in compasses wherein oil, glycerine, and other dense liquids are employed in lieu of air. The movement of the card produces currents, and the denser liquids acquire a momentum when set in motion which serves to deflect the needle.

The object of my invention is to remedy this defect, and for this purpose I cause the compasscard to move in a vacuum, so that being shielded from external influences the north pole of the magnetic needle will then always point truly to the north magnetic pole of the earth.

In carrying out my invention I cover the compass-bowl hermetically with a sheet of plate-glass of sufficient strength to bear the atmospheric pressure, and then, by means of an air-pump or suitable exhausting apparatus, I produce as perfect a vacuum as possible within the compass'bowl.

One method of producing and maintaining a vacuum in thecompass-box is represented in Figure 1 of the annexed drawings, which is a vertical section of a mariners compass.

a is the bowl, and Z) the card, pivotedin any ordinary manner.

0 is a sheet of plate-glass, with which the bowl is hermetically covered, and which is strong enough to bear the atmospheric pressure.

d is a screw-ring to secure the plate 0 in position.

In the bottom of the bowl I drill a vertical hole, 6, about one-eighth of an inch in diameter, more or less, also a horizontal hole, 6', of like diameter, extending from the side of June 28, 1881.

(No model.) Patented in England December 1, 1880.

the bowl to the bottom of the hole 6. I then make the hole 0 of conical form, as shown, and I insert into it a brass or other soft-metal tube, f,.the inner end of which I solder into the hole 6. The glass 0 having been secured in place, I connect the tubefwith an air-pump and produce a vacuum in the bowl a. When the vacuum is formed I compress the sides of the tube f, as indicated in dotted lines, by

means of pliers or other suitable tool, so as to hermetically close it, and I then sever the tube outside the compression, after which 1 solder up the hole 6 so as to make it flush with the surface of the bowl.

Fig. 2 represents in vertical section, and Fig. 3 in elevation, taken at right angles to Fig. 2, a somewhat modified way ofproducing and maintaining the vacuum in the compassbox.

9 is a hoop or ring which exactly fits the outside ofthe bowl. I drill a hole, 6 0, through the hoop g and through the side of the bowl a, and I screw or otherwise fix into the hole 6 in the hoop a tube,f, which I connect with the air-pump. After having produced the required vacuum in the bowl I turn the hoop g partly round, so as to bring an unperforated part opposite the hole 0, and thereby close the hole. To insure that the closing shall be hermetic, the part of the hoop moved over the hole may be faced with leather or other like suitable material. I then fix the hoop in place byrunning solder into the hole 6 andinto three or other suitable number of other holes, 0 which 1 form for the purpose in the hoop.

I am aware that a compass-box has been constructed with an annular wall around it, from the cavity in which the air has been abstracted, the object being to reduce the aberration resulting from local attraction; but I am not aware of a compass-card having been arranged to move in a vacuum, as herein described.

I am also aware that the movement of the needle-card in a vacuum will render it less stable and more sensitive than when it moves in air, or in some denser liquid, as oil or glycerine and should it be found too sensitive this may be corrected by an increase of friction at the pivot.

mounted rotatively on a pivot within said box, substantially as described.

In witness whereof I have hereunto signed my name in the presence of two subscribing Witnesses.

JAMES RE ADMAN.

Witnesses:

EDUARD HENDERSON, ISAAC GARNETT. 

